Wave generation and particle acceleration in electron-positron plasmas

The dynamics of an electron-position plasma cloud moving perpendicular to an ambient magnetic field with background plasmas is investigated by using a three-dimensional electromagnetic particle code. It is shown that the Alfven waves with large amplitude and linear polarization are excited dominantly, while the electromagnetic waves are weakly excited because of the relativistic effect of the cloud particles. When the cloud density becomes large, Langmuir waves leading to particle acceleration are also generated to compensate the charges escaping from the cloud along the magnetic field. Using a two-dimensional electromagnetic and relativistic particle code, it is shown that high-frequency Langmuir waves can be generated by the plasma maser mechanism from low-frequency Alfven waves excited by a temperature anisotropy. It is confirmed by the simulation that the plasma maser mechanism does not require an electron (or positron) beam component for the growth of Langmuir waves.